Nowadays, input/output ports of a microprocessor chip are widely used in a maximal matrix keyboard scan operation of a keyboard. On the chip, the input/output ports are used to execute the maximal matrix keyboard scan for controlling keys of the electronic organ. But under this condition, the keyboard input/output ports only can receive two inputs at the same time. If a third input is received from the keyboard, an error result of the keyboard scan might appear.
Please refer to FIG. 1. FIG. 1 shows the schematical view of the circuit of the prior art. FIG. 1 shows a 4×4 matrix 11 which is formed by means of cross-linking eight input/output ports, and thus there are sixteen inputs in the matrix 11. When any one of the sixteen inputs is pressed, the corresponding horizontal and vertical lines will electrically be conducted and then the input can be read by the chip 10, which is the theory applied to a keyboard scan. But there exists a defect in the keyboard scan circuit. The defect is that only two inputs can be pressed synchronously. If the third input is pressed and its position forms a right triangle with theses of the previous two pressed inputs, the corresponding fourth input will be scanned definitely and thereby an error decision will be produced. For example, when an user inputs a key 2, a key 3, and a key 7, consequently a key 6 will also be scanned automatically by the scanning program even though the user didn't input it. Thus there brings an error decision. This is a blind spot in the traditional keyboard scan circuit.
Because of the technical defects described above, the applicant keeps on carving unflaggingly to develop “scan circuit and method for keyboard” through wholehearted experience and research.